The use of safety devices for automatically preventing the traveling block of a drilling rig from being pulled into the crown or top of the drilling rig and which are actuated by the cable that is coiled around the cable drum in order to control the rig clutch and brake is generally shown in U.S. Pat. Nos. 2,683,020 and 3,677,520. Thus, as the traveling block is raised a predetermined distance, the cable is wound on the cable drum and increases the diameter of the cable drum and actuates an air toggle valve which in turn engages the rig brake thereby stopping the traveling block. However, the present invention is also directed to providing a safety device to provide protection when the traveling block has reached a predetermined bottom position, normally known as falling block condition. That is, the traveling block may be supporting thousands of pounds of drilling pipe and if the operator fails for any reason to properly stop the downward travel of the traveling block extensive and expensive damage may occur. The present invention is directed to the provision and incorporation into the drawworks control system of means to activiate the brake and shut down the clutch when the traveling block reaches a low predetermined position.